Effect of Head Position and Tube Entry on Corneal Endothelial Cells in Patients with Glaucoma Drainage Implants: A Cross-sectional Study

Abstract

Currently, reduction of intraocular pressure (IOP) is the only proven treatment for glaucoma [1]. IOP reduction can be achieved with medication, laser, or surgery. Surgical treatment for glaucoma includes trabeculectomy, glaucoma drainage device (GDD) implantation, trabecular bypass stents, ab interno trabeculectomy, and subconjunctival stenting [2-6]. The emergence of minimally invasive glaucoma surgery has broadened the scope of surgical alterna-Purpose: To investigate the effect of head tilt on the tube position of the Ahmed glaucoma valve (AGV) implanted in patients with glaucoma and to assess how the head tilt-induced alterations of tube parameters and the level of tube entry influence corneal endothelial cell density (ECD). Methods: A total of 29 eyes of 26 patients with AGV implantation were included. Tube-cornea distance, tube-cornea angle, and intracameral tube length were measured using anterior segment optical coherence tomography in three different head positions (neutral, 30° temporalward tilt, and 30° nasalward tilt). The tube entry was assessed using static gonioscopy. ECD was measured using specular microscopy before and after surgery. Results: The mean tube-cornea distance, tube-cornea angle, and intracameral tube length (neutral: 0.87 ± 0.39 mm, 30.56 ± 5.89˚, and 3.10 ± 0.82 mm, respectively) decreased with head tilts (temporalward: 0.82 ± 0.39 mm, 29.27 ± 5.82˚, and 3.04 ± 0.82 mm, respectively; nasalward: 0.83 ± 0.40 mm, 29.61 ± 6.04˚, and 3.05 ± 0.81 mm, respectively; all p < 0.01). The multivariate analyses found age and the tube insertion level to be associated with postoperative changes in the central ECD (p = 0.039 and 0.013, respectively), and the postoperative follow-up period and tube insertion level to be associated with the difference between the inferonasal and superotemporal ECDs (p = 0.034 and 0.007, respectively). Conclusions: Mild alterations of head positions induced changes in the intracameral tube positions of AGV implants; nevertheless, it did not significantly affect ECD loss. However, the eyes with tubes inserted anteriorly to Schwalbe's line may be more susceptible to corneal ECD loss.

The long-term effects of the first and second glaucoma drainage implant surgery in patients with primary open-angle glaucoma

“…Warning the patient of possible redness on the limbus at the insertion site of the tube may also be important if the patch becomes thin or melted. Several previous studies have reported on a loss of CEC density post GDIS, which is thought caused by physical contact of the tube to the cornea at its insertion point [28], the distance of the tube tip to the cornea [29], a change in the location of the tube during the postoperative time course [30], a foreign body reaction against the tube material [31], or turbulence at the tip of the silicon tube [32]. Kim et al [33] reported that post AGV implantation, the mean loss of CEC density per month was 17.5 cells/mm 2 (0.84%), while that reported by Zhang et al [34] was 29.3 cells/mm 2 (1.37%).…”

The effects of the first versus second glaucoma drainage implant surgery in patients with primary open-angle glaucoma

“…Several previous studies have reported on a loss of CEC density post GDIS, which is thought caused by physical contact of the tube to the cornea at its insertion point [ 29 ], the distance of the tube tip to the cornea [ 30 ], a change in the location of the tube during the postoperative time course [ 31 ], a foreign body reaction against the tube material [ 32 ], or turbulence at the tip of the silicon tube [ 33 ]. Kim et al [ 34 ] reported that post AGV implantation, the mean loss of CEC density per month was − 17.5 cells/mm 2 (0.84%), while that reported by Zhang et al [ 35 ] was − 29.3 cells/mm 2 (1.37%).…”